Solid fossil fuels such as coal often are ground in order to render the solid fossil fuel suitable for certain applications. Grinding the solid fossil fuel can be accomplished using a device referred to by those skilled in the art as a pulverizer. One type of pulverizer suited for grinding is referred to as a “bowl mill pulverizer” 10 as shown in FIG. 1. This type of pulverizer obtains its name by virtue of the fact that the pulverization that takes place on a grinding table 14 that resemblance to a bowl.
The bowl mill pulverizer 10 includes a substantially closed separator body 12. A grinding table 14 is mounted on a shaft 16. A motor and gearbox drive mechanism (not shown) rotate the grinding table 14. These components arranged within the separator body 12.
A plurality of journal assemblies 19 and grinding rolls 18, preferably three, are supported within the separator body 12 so as to be equidistantly spaced one from another around the circumference of the separator body 12. Only one journal assembly 19 and grinding roll 18 of three is shown in FIG. 1. Each of the grinding rolls 18 is supported and rotates on a suitable shaft (not shown) of a journal assembly 19. The journal assemblies 19 and grinding rolls 18 are allowed to pivot away from the grinding table 14 by the trunnion shaft 36.
Each of the grinding rolls 18 has a spring assembly 20 acting on the journal head 70 of the journal assembly 19. Each of the spring assemblies 20 applies a spring load on the corresponding grinding roll 18 causing them to pivot on trunnion shaft 36 and to exert the requisite degree of force on the solid fuel on the grinding table 14 pulverizing the solid fuel into powder.
The solid fuel is provided through fuel inlet tube 22 and falls through to grinding table 14 to be pulverized.
After being pulverized, the particles of the solid fuel are thrown outwardly by centrifugal force, whereby the particles are fed into a stream of warm air and blown into a classifier 30 for separation by particle size. The particles of the proper size are passed out of outlets 34.
The larger particles fall downward through outlet 28 for more grinding. The greater the force, the finer the particle size of the fossil fuels being ground.
There are devices which provide feedback regarding the amount of force being applied to each grinding roll 18 as described in U.S. patent application Ser. No. 12/490,668 filed Jun. 24, 2010 “Force Monitor For Pulverizer Integral Spring Assembly”. This does not however, indicate angular displacement of the trunnion shafts 36 and journal assemblies 19.
The forces acting on the journal assembly 19 are the spring force, which forces the journal assembly downward, and the reaction force of the grinding roll upon the solid fuel bed contained on the grinding table 14, which forces the journal assembly upward and downward, creating the oscillations. There are normal oscillations that occur within an acceptable range, however, there are also abnormal oscillations indicating a problem with the pulverizer.
The force measured by load cells do not directly relate to the displacement of the journal assemblies 19. This is because the forces provided by the springs typically do not have a linear relationship with displacement.
The linear change in the spring is related to many thousands of pounds of force. Therefore, it is not very accurate in measuring small forces that have small angular displacements.
Also, the force v. displacement curve exhibited by a spring changes over time as the spring ages.
Due to the non-linear relationship between displacement and force and the fact that springs change their displacement vs. force curve for several reasons, monitoring linear spring displacement relating to oscillations can be inaccurate.
The information that is currently available on conventional pulverizers is the initial spring force (initial spring compression) which is set on each journal spring assembly prior to the pulverizer being placed into service and the initial clearance set between the grinding roll 18 and grinding table 14 (the “roll-ring clearance”).
For journal assemblies 19 of shallow bowl type pulverizers, an additional piece of known information is the clearance between a journal head 70 and the seat of the spring assembly 20. However, the accuracy by which each of these items is set is dependent on the skill of the workers, the accuracy of the equipment and gages used by the workers, and the method the worker use to perform the work.
Presently, there is little or no instrumentation present to measure these oscillations. The journal assemblies 19 are currently evaluated visually by watching the end face of the trunnion shaft 36 and comparing its movement to the vibration of the bowl mill pulverizer 10.
This is a crude method and the ability to obtain useful results from it is highly dependent on the experience of the personnel who perform it.
The result is that operation problems or failure of the pulverizer, its grinding components, or its gearbox components can occur before the conditions responsible for creating the problems are noticed and corrected.
Currently, there is a need for feedback to more accurately monitor various abnormalities of a pulverizer.